Dept of Pediatrics, U of OK College of MedicineOklahoma Medical Research Foundation

Objective:

Our previous work has shown that there are distinct gene expression profiles in peripheral blood mononuclear cells (PBMC) and in granulocytes derived from patients with polyarticular juvenile idiopathic arthritis (JIA) compared with healthy control children of the same age and sex. Network analysis of these differentially expressed genes demonstrates that many of those genes are under the control of a single transcription factor, hepatocyte nuclear factor alpha (HNF4A). Furthermore, HNF4a appears to determine both response to therapy and achievement of remission. However, HNF4a has not previously been known to be expressed in leukocytes. To understand the role of HNF4a in JIA, we examined its expression in PBMC subsets and granulocytes.

Method:

PBMC, CD4+ T cells, CD8+ T cells, CD14+ monocytes, CD19+ B cells and granulocytes were isolated using conventional methods. RNA was separately extracted and reverse transcription- polymerase chain reaction was used to detect the expression of HNF4a mRNA. Immunofluorescence staining and confocal microscopy were used to observe the expression of HNF4a protein. The DECODE database (SABiosciences Company) was used to search HNF4A binding sites within the differentially expressed genes.

Results:

Polymerase chain reaction (PCR) analyses revealed that expression of HNF4a mRNA is leukocyte subset-dependent. PBMC, T cells and granulocytes, but not not CD14+ monocytes or CD19+ B cells, express HNF4a mRNA. Immunofluorescence staining for HNF4a was used to detect HNF4a in leukocyte subsets. HNF4a is expressed in granulocytes in a distinct pattern demonstrating two cell subsets. The first population observed on on confocal microscopy consisted of CD66b bright/HNF4a dim cells, and the second consisted of HNF4a bright/CD66b dim cells. In T cells, the HNF4a signal was significantly brighter in CD8+ cells than in CD4+ cells. All of these findings were observed in healthy children, healthy adults, and children with JIA. Thus, expression of HNF4a is not in itself pathological, and HNF4a may an important and previously unrecognized regulatory protein. Bioinformatics analysis of the promotor regions of ZNF281, IER5 and OAZ2, genes shown in Ingenuity analysis of PBMC array data from children with JIA to be under HNF4a transcriptional control, demonstrated sequence motifs typically associated with HNF4a binding.

Conclusion:

HNF4A is an important systems hub that emerges from microarray analysis of JIA leukocytes. This transcription factor, which has not previously been demonstrated in leukocytes, may play a role in both disease pathogenesis and response to therapy. Expression of HNF4a was found in CD4+ and CD8+ T cells and neutrophils and was seen in both healthy children and children with JIA. Given the potential importance of HNF4a is regulating response to therapy in JIA, we believe that these studies may shed light on potential new targets of therapy in this challenging disease.